Liquid-crystal lenses with variable refractive index have heretofore been proposed. For example, a liquid-crystal lens including a single liquid-crystal layer generally refracts only a specific polarized light component and does not refract the other polarized light components. Therefore, it is necessary to dispose a polarizing plate in front of the liquid-crystal lens so that only the specific polarized light component to be refracted by the liquid-crystal layer can enter the liquid-crystal layer. This presents a problem of significant light intensity loss.
In view of the foregoing problem, for example, Patent Literature 1 proposes to obtain a liquid-crystal lens requiring no polarizing plate by disposing a first liquid-crystal lens and a second liquid-crystal lens to have their respective alignment directions orthogonal to each other in a plane perpendicular to the optical axis.
In addition, Patent Literature 1 also proposes that one of the first liquid-crystal lens and second liquid-crystal lens close to the image plane has a smaller focal length than the other liquid-crystal lens close to the object. Patent Literature 1 describes that by doing so, for example, the gap between the locations of images formed by P-polarized light and S-polarized light can be reduced to achieve excellent imaging performance.